The present invention is directed to an improved method of generating visible light and to an improved bulb and lamp for providing such light.
U.S. Pat. Nos. 5,404,076, and 5,606,220, and PCT Publication No. WO 92/08240, which are incorporated herein by reference, disclose lamps for providing visible light which utilize sulfur and selenium based fills. Co-pending U.S. application Ser. No. 08/324,149, filed Oct. 17, 1994, now U.S. Pat. No. 5,661,365 also incorporated herein by reference, discloses similar lamps for providing visible light which utilize a tellurium based fill.
These sulfur, selenium and tellurium lamps of the prior art provide light having a good color rendering index with high efficacy. Additionally the electrodeless versions of these lamps have a very long lifetime.
Most practical embodiments of sulfur, selenium, and tellurium lamps have required bulb rotation in order to operate properly. This is disclosed in PCT Publication No. WO 94/08439, where it is noted that in the absence of bulb rotation, an isolated or filamentary discharge results, which does not substantially fill the inside of the bulb.
The requirement of rotation which was generally present in the prior art lamps introduced certain complications. Thus, the bulb is rotated by a motor, which has the potential for failure, and which may be a limiting factor on the lifetime of the lamp. Furthermore, additional components are necessary, thereby making the lamp more complex and requiring the stocking of more spare parts. It therefore would be desirable to provide a lamp affording the advantages of the prior sulfur, selenium and tellurium lamps, but which does not require rotation.
PCT Publication No. WO 95/28069, a Dewar lamp was disclosed for purportedly obviating rotation. However, a problem with such Dewar configuration is that it is complicated in that it utilizes peripheral and central plated electrodes on the bulb, and the central electrode is prone to overheating.